Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07H—SUGARS; DERIVATIVES THEREOF; NUCLEOSIDES; NUCLEOTIDES; NUCLEIC ACIDS
  • C07H17/00—Compounds containing heterocyclic radicals directly attached to hetero atoms of saccharide radicals
  • C07H17/04—Heterocyclic radicals containing only oxygen as ring hetero atoms
  • C07H17/08—Hetero rings containing eight or more ring members, e.g. erythromycins

Definitions

• the present invention relates to erythromycin derivatives. More particularly, the present invention pertains to erythromycin A 9-oximesilyls and their use in the production of 6-O-alkyl erythromycin A derivatives.
• 6-O-alkyl derivatives of erythromycin A have use as antibacterial agents.
• 6-O-methylerythromycin A (clarithromycin), shown below, is a potent macrolide antibiotic (U. S. Patent No. 4,331,803).
• 6-O-methylerythromycin A can be prepared by methylating a 2 ' -0-3 ' -N-dibenzyloxycarbonyl-des-N-methyl derivative of erythromycin A (U. S. Patent No. 4,331,803). 6-O-methylerythromycin A can also be made from 9-oxime erythromycin A derivatives (See, e.g., U. S. Patent Nos. 5,274,085; 4,680,386; 4,668,776; 4,670,549 and 4,672,109 and European Patent Application 0260938 A2).
• the oxime is protected during methylation with a 2-alkenyl group (U. S. Patent Nos. 4,670,549 and 4,668,776), a benzyl or substituted benzyl group (TJ. S. Patent Nos. 4,680,386, and 4,670,549) or a moiety selected from the group consisting of lower alkyl, substituted alkyl, lower alkenyl, aryl substituted methyl, substituted oxalkyl, and substituted thiomethyl (U. S. Patent No. 4,672,109).
• a trimethylsilyl group they are too unstable during methylation under alkaline conditions. (/. of Antibiotics, Vol. 46, No. 6, p. 647, 1993).
• Patent No. 4,670,549 discloses protection of the 2 -OH group as a benzyl or like substituent. Under these circumstances, the 3 -nitrogen group must also be protected as a quaternary salt. This quaternary salt must be removed following 6-O-methylation to regenerate the 3 -dimethyl amino group.
• the use of benzyloxycarbonyl groups for protection of the 2 ' -hydroxy group U. S. Patent No. 4,311,803 requires large amounts of benzyl chloroformate, which is severely irritating and toxic. Deprotection of 9- oxime protected with oxyalkyls has to be carried out in harsh conditions, which lead to undesired side product formation. There continues to be a need to provide a rapid, efficient method of producing 6-O-alkylerythromycin A that uses mild, neutral reaction conditions.
• the present invention provides an efficient and practical method of synthesizing 6-O-alkyl-erythromycin A derivatives.
• the synthetic process starts with a 9-oxime erythromycin A derivative which, by definition, includes a 6-hydroxy group.
• the derivative is converted to a 9-oximesilyl erythromycin A derivative, which is O-protected at the 2'-OH position and then selectively alkylated at the 6-oxygen.
• the 6-O-alkylated derivative is then desilylated and deoximated to give a 6-O-alkylerythromycin A.
• the 9-oximesilyl erythromycin A derivative is prepared by reacting a 9- oxi e erythromycin A derivative with a silylating agent to form an O- protected-oxime having a protecting group of the formula:
• R', R", and R' are independently hydrogen, lower alkyl, aryl, phenyl, phenyl substituted lower alkyl, cycloalkyl or alkenyl.
• a 9-oxime erythromycin A derivative used in a process of the present invention can be unsubstituted at the 2'-OH and 4'-OH positions or can contain a conventional O-protecting group at those positions.
• O-protecting groups include silyl (SiR'R"R '" , where R ' , R " and R '" are as defined above), acyl, lower alkenyl monocarbonyl, lower alkoxycarbonyl-alkylcarbonyl, and arylcarbonyl groups.
• the 9-oxime derivative can also be unsubstituted at the 3 ' -dimethyl- amino position or can contain a convention N-protecting group at that position.
• exemplary and preferred N-protecting groups are alkoxycarbonyl groups, alkoxyalkoxycarbonyi groups, haloalkoxycarbonyl groups, unsaturated alkoxycarbonyl groups, substituted benzyloxycarbonyl groups, substituted phenoxycarbonyl groups, and the like.
• the present invention also relates to novel intermediates useful in the preparation of 6-alkylerythromycin A.
• Those intermediates are 9-oximesilyl derivatives that are alkylated at the 6-position and unsubstituted or substituted at the 2'-, 3 - and/or 4"- positions.
• FIG. 1 shows one embodiment of a process of preparing 6-O-methyl erythromycin A.
• the present invention provides a process of preparing a 6- O- alkyl derivative of erythromycin A. That process includes the steps of converting a 9-oxime erythromycin A derivative into a 9-oximesilyl erythromycin A derivative and reacting the 9-oximesilyl erythromvcin A derivative with an alkylating agent.
• a process of the present invention begins with a 9-oxime erythromycin A derivative.
• 9-Oxime derivatives are prepared using standard procedures well known in the art. Briefly, an erythromycin A derivative is reacted with either hydroxylamine hydrochloride and a base, free hydroxylamine in methanol or hydroxylamine and an organic acid (See, e.g., U. S. Patent No. 5,274,085, the disclosure of which is incorporated herein by reference).
• the 9-oxime erythromycin A derivative is silylated by reacting the derivative with a silylating agent.
• a preferred silylating agent has the formula:
• R', R", and R' are independently hydrogen, lower alkyl, aryl, phenyl, phenyl substituted lower alkyl, cycloalkyl or alkenyl and X is a halogen or a sulfonate (e.g., mesylate, tosylate).
• a suitable organic base such as triethylamine (Et 3 N), pyridine, imidazole or di-trimethylsilyl amine [HN(TMS) 2 ].
• Another exemplary silylating agent has the formula:
• R', R " , and R'" are defined above.
• the silylating reaction can also be carried out in the presence of a suitable acid such as HCO2H.
• a suitable acid such as HCO2H.
• HCO2H a suitable acid
• to efficiently and selectively alkylate erythromycin A at the 6-OH position the hydroxyl groups at the 2 - and/or 4"- positions should be protected prior to methylation. It may also be desirable to protect the 3 -dimethylamino moiety. Such protection is accomplished by protecting those groups with conventional O- or N- protecting groups. The order of protection of 9-oxime and 2 ' , 4 " - OH groups can be exchanged.
• a 9-oximesilyl erythromycin A derivative formed during a synthetic process of the present invention corresponds to the structure I, below:
• R ' , R " and R' " are as defined above;
• R 2 and R 4 are each independently hydrogen or a conventional O-protecting group,
• R 3 is -NR 5 CH3, where R 5 is methyl (CH3) or a conventional N-protecting group or -N (CH )2R 6 X " , where R 6 is 2-alkenyl, benzyl or substituted benzyl, and X is a halogen such as Br, Cl or i.
• the compound of structure I is shown without spatial bond orientation. Structure I, thus, defines all combinations of bond orientation and is intended to cover all possible stereo-configurations (e.g., epimers). In a preferred embodiment, the bond orientations of Structure I are the same as shown above for 6-O-methylerythromycin A.
• the 9-oxime erythromycin A derivative is unsubstituted (unprotected) at the 2'-, 3 ' and 4 " -positions. Silylation of such a derivative results in formation of a 9-oximesilyl derivative of structure I, where R 2 and R 4 are both hydrogen and R 3 is methyl.
• the 9-oxime erythromycin A derivative used in the synthetic process has conventional O-protecting groups at the 2 - and 4 "- positions.
• O-protecting groups for protecting hydroxyls from alkylation are well known in the art and include silyl, acyl, lower alkenyl monocarbonyl, alkoxycarbonyl, alkylcarbonyl, lower alkoxycarbonylalkyl- carbonyl, and arylcarbonyl groups.
• Silylation of such a substituted 9-oxime erythromycin A derivative results in a 9-oximesilyl derivative of structure I, where R 2 and R 4 are silyl, carbonyl, acyl, alkoxycarbonyl, alkylcarbonyl, lower alkenyl monocarbonyl, lower alkoxycarbonylalkylcarbonyl, or arylcarbonyl.
• O-protecting groups are alkoxycarbonyls (e.g., methoxycarbonyl, ethoxycarbonyl, isopropoxycarbonyl, n-isopropoxycarbonyl, n-butyloxy-carbonyl, isobutyloxycarbonyl, sec-butyloxycarbonyl, t-butyloxy- carbonyl, 2-ethylhexyloxycarbonyl, cyclohexyloxycarbonyl, methyloxycarbonyl and the like), alkoxyalkoxycarbonyls (e.g., methoxymethoxycarbonyl, ethoxymethoxycarbonyl, 2-methoxyethoxycarbonyl, 2-ethoxyethoxycarbonyl, 2- butoxyethoxycarbonyl, 2-methoxyethoxy-methoxycarbonyl and the like), haloalkoxycarbonyls ⁇ e.g., 2-chloroethoxy-carbonyl, 2-ch
• Exemplary and preferred lower alkyl monocarbonyl groups are acetyl, propionyl, butyryl, isobutyryl and the like.
• Exemplary and preferred lower alkenyl monocarbonyl groups include acryloxyl, methacryloxy and the like.
• Exemplary and preferred lower alkoxycarbonyl-alkylcarbonyl groups include methoxycarbonyl-methylcarbonyl, ethoxycarbonylmethylcarbonyl, ethoxycarbonyl-ethylcarbonyl and the like.
• Exemplary and preferred arylcarbonyl groups include benzoyl, p-methoxybenzoyl, 3,4,5-trimethoxy- benzoyl, p-chlorobenzoyl, 2,4-dichlorobenzoyl, 3,5-dichlorobenzoyl, diphenylacetyl, 1-naphthaleneacetyl, 2-naphthaleneacetyl and the like.
• Exemplary and preferred silyl groups have the formula:
• a trimethyl silyl group can be positioned at the 2'- and 4"-positions by reacting a 9-oxime erythromycin A derivative with the silylating agent hexamethyl- disilane (HMDS) in the presence of acid (e.g., HCO2H).
• HMDS hexamethyl- disilane
• TMSCl trimethylsilylchloride
• An acetyl group can be positioned at the 2'- and 4"-posi tions by reacting an erythromycin A derivative (9-oxime or 9-oximesilyl) with an acetylating agent and a base.
• Suitable acetylating agents that can be used include anhydride and acid halide compounds of the formula (R COhO or R 5 COCl, where R 5 is hydrogen or a substituent group such as lower alkyl (e.g., methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, t-butyl and the like) or aryl (e.g., phenyl, p-methoxyphenyl, p-chlorophenyl, m-chlorophenyl, o-chlorophenyl, 2,4,-dichlorophenyl, p-bromophenyl, m-nitrophenyl, p-
• N-protecting groups are alkoxycarbonyl groups (e.g., a methoxycarbonyl group, an ethoxycarbonyl group, an isopropoxycarbonyl group, an n-propoxycarbonyl group, an n- butoxycarbonyl group, an isobutyloxycarbonyl group, a sec-butyloxycarbonyl group, a t-butyloxycarbonyl group, a 2-ethylhexyloxycarbonyl group, a cyclohexyloxycarbonyl group, a methyloxycarbonyl group and the like); alkoxyalkoxycarbonyi groups (e.g., a methoxymethoxycarbonyl group, an ethoxymethoxycarbonyl group
• the dimethylamino moiety at the 3 -position may also be protected as a quaternary salt by reacting it with a derivative R-X, wherein R is a 2-alkenyl group, a benzyl group or a substituted benzyl group; and X is a halogen atom (See, e.g., U. S. Patent No. 4,670,549).
• R is a 2-alkenyl group, a benzyl group or a substituted benzyl group
• X is a halogen atom
• a compound of Structure I is reacted with a suitable alkylating agent in the presence of a base.
• suitable alkylating agents are methyl bromide, ethyl bromide, n-propyl bromide, methyl iodide, ethyl iodide, n-propyl bromide, dimethyl sulfate, diethyl sulfate, di-n-propyl sulfate, methyl-p-toluenesulfonate, ethyl methanesulfonate, n-propyl methanesulfonate and alkyl triflates.
• Exemplary and preferred bases are a strong alkali metal base, preferably selected from the group consisting of an alkali metal hydride, alkali metal hydroxide or alkali metal alkoxide, and a weak organic amine base, preferably selected from the group consisting of trimethylamine, triethylamine, tripropylamine, pyridine, 2-methoxypyridine, 1-methylpyrrolidine, 1- methylpiperidine, and 1-ethylpiperidine.
• a strong alkali metal base preferably selected from the group consisting of an alkali metal hydride, alkali metal hydroxide or alkali metal alkoxide
• a weak organic amine base preferably selected from the group consisting of trimethylamine, triethylamine, tripropylamine, pyridine, 2-methoxypyridine, 1-methylpyrrolidine, 1- methylpiperidine, and 1-ethylpiperidine.
• the methylation step is carried out in a suitable solvent.
• suitable solvents are polar aprotic solvents such as N,N-dimethyl- formamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, hexamethyl- phosphoric triamide, tetrahydrofuran, 1,2-dimethoxyethane, acetonitrile, ethyl acetate or methyl-t-butyl ether, or a mixture of such polar aprotic solvents maintained at a reaction temperature and for a period of time sufficient to effect alkylation, preferably from -15 °C to room temperature for a period of 1 to 8 hours.
• the preferred solvent includes at least methyl-t-butyl ether.
• R ' , R " , R '" , R 2 , R 3 and R 4 are as defined above for structure I.
• the preparation of 6-O-alkylerythromycin A proceeds by removing the O-protecting groups from the 2 ' - and 4 " -positions and the silyl group from the 9-oximesilyl and then deoximating the 9-oxime.
• Means for removing the O- protecting groups at the 2 - and 4"-positions are well known in the art and depend upon the nature of the protecting group.
• the acetyl group can be removed by reacting the acetylated derivative with a compound of the formula R 6 OH, where R 6 is alkyl (e.g., methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, t-butyl and the like).
• R 6 is alkyl (e.g., methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, t-butyl and the like).
• the reaction can take place in the absence or presence of an acid ⁇ e.g., formic acid, acetic acid) or water, or can take place in the absence or presence of a base (e.g., K2CO3, Na2C ⁇ 3, KHCO3, NaHC ⁇ 3).
• the silyl group can be removed by reacting the silylated derivative with formic acid (HCO2H) in isopropyl alcohol (IPrOH).
• HCO2H formic acid
• IPrOH isopropyl alcohol
• Removal of the silyl group from the 9-oximesilyl is accomplished using the same procedures as set forth above in relation to removal of the silyl group from the 2'- and/or 4 " -positions. It is advantageous to use a silyl group for protection of the 2 - and 4 " -positions because deprotection of those groups can occur in the same step as removal of the silyl group from the 9-oximesilyl. Still another advantage of using silyl groups is that deprotection (desilylation) can be accomplished using mild (room temperature), neutral conditions. A final step in the preparation of a 6-O-alkyl erythromycin A is deoximation. Deoximation is carried out in accordance with standard procedures well known in the art (See e.g., U.
• Compound 2 is then reacted with a silylating agent (R3SiCl) in the presence of triethylamine (Et3N) and tetrahydrofuran (THF) to form a 2 ' , 4"- bis-trimethylsilyl, 9-oximesilyl erythromycin A derivative (Compound 3).
• Methylation of the 6-OH is then carried out by reacting Compound 3 with a methylating agent (MeX) and sodium hydride (NaH) in an appropriate solvent [dimethylsulfoxide (DMSO) and THF] to form a 2', 4"-di-trimethylsilyl, 6-O-methyl, 9-oximesilyl erythromycin A derivative (Compound 4).
• the silyl groups at the 2', 4 " - and 9-positions are removed by reacting Compound 4 with BU4NF in THF to form a 2', 4"-dihydroxyl, 6-O-methyl, 9-oxime erythromycin A derivative (Compound 5).
• Compound 5 is then deoximated to yield 6-O- methylerythromycin A (clarithromycin).
• the present invention also provides 9-oximesilyl derivatives of erythromycin A, which derivatives are intermediates in the synthesis of 6-O- alkylerythromycin A.
• a 9-oximesilyl derivative of the present invention can be alkylated or unsubstituted at the 6-position (i.e., 6-OH or 6-O-alkyl), unsubstituted ⁇ i.e., 2 ' -OH, 4 " -OH, 3 ' -dimethyl) or substituted at the 2 ' , 4 " or 3 ' - positions with a conventional protecting group as set forth above.
• a 9-oximesilyl erythromycin A derivative of the present invention corresponds to the structure I or II.
• the product was extracted with t-butyl methyl ether and the organic layer was washed with a saturated sodium chloride solution. It was then dried over Na2S ⁇ 4 and concentrated under reduced pressure to give a crude product.
• the crude product was dissolved in a mixture of 20 ml of hexane and 10 ml of acetonitrile. The upper hexane layer was separated and concentrated under reduced pressure to yield 810 mg of 2',4"-0-bis(trimethylsilyl)-6-0-methylerythromycin A 9-(0- triisopropylsilyl) oxime which was used in the desilylation step without further purification.
• the product can be further purified by recrystallization from MeOH. The structure was confirmed by NMR and mass spectra.
• the product was extracted with t-butyl methyl ether and the organic layer was washed with a saturated sodium chloride solution, dried over Na2SO4 and concentrated under reduced pressure to give a crude product.
• the crude product was dissolved in a mixture of 20 ml of hexane and 10 ml of acetonitrile.
• the upper hexane layer was separated and concentrated under reduced pressure to yield 805 mg of 2',4"-0-bis(trimethylsilyl)-6-0-methylerythromycin A 9(0- triisopropylsilyl) oxime which was used in the desilylation step without further purification.
• the product can be further purified by recrystallization from MeOH. The structure was confirmed by NMR and mass spectra.

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• 1996
  • 1996-04-02 US US08/626,524 patent/US5837829A/en not_active Expired - Lifetime
• 1997
  • 1997-02-06 EP EP97905826A patent/EP0891371B1/en not_active Expired - Lifetime
  • 1997-02-06 PT PT97905826T patent/PT891371E/pt unknown
  • 1997-02-06 WO PCT/US1997/001955 patent/WO1997036913A1/en active IP Right Grant
  • 1997-02-06 ES ES97905826T patent/ES2212808T3/es not_active Expired - Lifetime
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  • 1997-02-06 JP JP9535252A patent/JP2000507574A/ja not_active Withdrawn
  • 1997-02-06 CA CA002250771A patent/CA2250771C/en not_active Expired - Fee Related
  • 1997-02-06 DE DE69726714T patent/DE69726714T2/de not_active Expired - Fee Related
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